It is earlier known to add precut steel fibres to a concrete mass, which by means of concrete spraying is applied to the surface intended. The fibres have then been added in a concrete mixer or the like. The mixture thereupon has been placed in a spraying machine, whereupon it has been brought to an orifice and has been sprayed out onto a desired base.
It has proved itself that the above described type of addition of fibres to the concrete mass, limits the achievable fibre content in the mass to one or some percent of volume only, as the fibres during the mixing and the transport together with ballast and cement material has a tendency to ball or become packed together in lumps. It has therefore been necessary to use low fibre contents at the mixing, whereby the desired improvements regarding strength, fracture dispersion, deformation ability etc. cannot be achieved or will be achieved to a very limited extent only. The desired alignment of the fibres in mainly one direction is not obtained, but the fibres will randomly arrange themselves in three dimensions, whereby the reinforcing effect is essentially reduced.
It has earlier been proposed to supply the fibre material to the dry cement and ballast material in an air stream and this method has proved itself to be very successful. The steel or metal fibres are however available on the market only as short, cut pieces, which are packed together in lumps in such a manner that the fibres only with great difficulty can be separated from each other.
The purpose of the present invention is now to propose a method and a device for preparing the fibres so that they with elimination of the above mentioned drawbacks in a correct and controllable manner can be supplied to the material stream at concrete spraying. This problem has been solved thereby that the fibre bundles or fibre lumps, are disintegrated into separate fibres in a defibrating apparatus by being shredded, shaken, cut and/or tumbled in a sieve and/or a tumbler, that the separate fibres are dosed and that the separate fibres are aligned with the longitudinal direction of the fibres being essentially parallel to their direction of transport by means of unobstructed downfall upon an inclined surface followed by paralleling in an air stream in a transport duct.
This is achieved with a device comprising in combination a defibrating apparatus, designed mechanically to separate the fibres from each other, a dosing apparatus for feeding out the fibres in dosed quantities and an alignment unit for arranging the fibres in three planes and a transport duct connected to the alignment unit and provided with means for generating therein an air stream as a transport medium for the fibres.